Microwave dielectric ceramic composition

ABSTRACT

A microwave dielectric ceramic composition exhibiting excellent relative permitting (∈) and high Qf-value, enabling the temperature coefficient of resonance frequency to be easily adjusted, and being best suited for a filter having cavities made of, e.g., iron or copper exhibiting a large temperature coefficient of resonance frequency. The ceramic is of a BaO—TiO 2 —Nd 2 O 3 —Sm 2 O 3  ceramic, type wherein Nd 2 O 3  is partly substituted by Bi 2 O 3 , Nd 2 O 3  is Partly substituted by Ln 2 O 3  (where Ln is La, Ce or Pr) and, the above substituted Ln 2 O 3  is partly substituted by EU 2 O 3  to improve the properties so that ∈ is 82.5 to 92.5, Qf is 6000 to 7300 GHz and τf is 10-20 ppm/° C. This makes it possible to impart favorable electric characteristics to resonance cavities of various materials and sizes.

This is a 371 of PCT/JP98/02467 filed Jun. 4, 1998.

DESCRIPTION

1. Technical Field

The present invention relates to a dielectric ceramic composition whosechief constituents are Ba, Ti, Sm. Nd, La, Ce, Pr, Bi and O₂,additionally containing Eu₂O₃ and having the properties ∈=82.5 to 92.5,Qf=6000 to 7300 GHz, τf=10 to −20 ppm/° C. which is capable of beingemployed as a dielectric resonance material or frequency adjusting rodthereof.

2. Background Art

In recent years, with the development of new media in the field ofelectronic technology, there has been rapid progress in miniaturizationand digitization. In particular, in the field of communications usingmicrowaves such as satellite communication, car phones, and mobiletelephones, advanced miniaturization of components and high levels ofreliability are being demanded.

In conventional microwave circuits cavity resonators or waveguides areemployed as filter or transmission circuits so this has presented anobstacle to such miniaturization and enhanced reliability. Specifically,in cavity resonators or waveguides, basically the stability of air orvacuum as a propagation medium for electromagnetic waves is made use of;in order to miniaturize a microwave circuit portion as aforesaid, apropagation medium may be employed which has a larger dielectricconstant than the dielectric constant of air or vacuum and which has thesame level of high stability in respect of temperature as air or vacuum.If this is done, the propagation wavelength of the microwaves in themedium is 1/{square root over ((∈r))} (where ∈r is the relativepermittivity), so the resonant wavelength is also 1/{square root over((∈r))} and miniaturization can be achieved.

Previous microwave dielectric ceramic compositions that have beenproposed include BaO—TiO₂—Nd₂O₃—Bi₂O₃ based ceramics (Laid-open JapanesePatent Publication Sho. 56-102003) and BaO—TiO₂—Sm₂O₃—CeO₂—Bi₂O₃ basedceramics (Laid-open Japanese Patent Publication Sho. 62-187162).However, these materials suffered from the problems of their Qf value asa microwave communication dielectric being low at 4000 to 6500 and thatadjustment of the temperature characteristic of frequency for variouscavities was not easy.

Also, BaO—TiO₂—Ln₂O₃ based ceramics (where Ln₂O₃ represents addition ofCr₂O₃ to Nd₂O₃ or Pr₆O₁₁) (Japanese Laid-open Patent Publication H.7-169326) have a relative permittivity value (∈) of 91 to 93, but theywere subject to the problems that their Q value is low at 5700 to 6000,and their temperature coefficient τf of resonance frequency is 6 to 9ppm/° C., so that they cannot be employed in filters where the cavitymaterial has a large temperature coefficient of resonance frequency,such as iron or copper.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a microwave dielectricceramic composition whereby the problems of the prior art microwavedielectric ceramic composition are solved, which is of excellentrelative permittivity (∈) characteristic, has a high Qf value, wherebyadjustment of the temperature coefficient of the resonance frequency caneasily be achieved, and which is ideal for filters where the cavitymaterial has a large temperature coefficient of resonance frequency,such as iron or copper.

As a result of various studies of ceramic compositions with the objectof providing a microwave dielectric ceramic composition of high Qf valueand of improved temperature characteristic, the present inventorsdiscovered that the properties: ∈=88.5 to 92.5, Qf=6000 to 7300 GHz,τf=3 to −10 ppm/° C. could be obtained by, in a BaO—TiO₂—Nd₂O₃—Sm₂O₃based ceramic, substituting some of the Nd₂O₃ by Bi₂O₃ and furthersubstituting some of the Nd₂O₃ by Ln₂O₃ (where Ln=La, Ce, Pr).

Furthermore, they discovered that, by substituting some of theaforementioned substituted Ln₂O₃ with Eu₂O₃, a material could beprovided with temperature coefficient τf of resonance frequency improvedto 10 to −20 ppm/° C. and furthermore, the foregoing material may besintered in the atmosphere; however, they discovered that, by sinteringin an atmosphere containing at least 80% of oxygen, excellent propertiesin respect of the Qf value and/or τf value mentioned above are provided,and in addition the permittivity ∈ of frequency is improved to 82.5 to92.5, thereby perfecting the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention consists in a microwave dielectric ceramiccomposition whose compositional formula is represented by:

Ba_(6−3x)·{Sm_(1−y)·(Nd_(1−w−v)Eu_(w)Ln_(v))_(y−z)Bi_(z)}_(8+2x)·Ti₁₈O₅₄(where Ln=La,Ce,Pr)

where the values of x, y, z, y−z, w and v in the compositional formulasatisfy the following values:

0.5<x<0.8, 0.3<y<0.5, 0<z<0.4, y−z>0, 0<w≦1,0<v≦1.

The reasons for the restrictions in the composition of the presentinvention will now be described. In a dielectric ceramic composition ofcompositional formulaBa_(6−3x)·{Sm_(1−y)·(Nd_(1−w−v)Eu_(w)Ln_(v))_(y−z)Bi_(z)}_(8+2x)·Ti₁₈O₅₄,if x is less than 0.5, the Q value of the dielectric falls; if it ismore than 0.8, the permittivity falls; these are therefore undesirable.Also, if y is less than 0.3, this tends to cause a drop in permittivity,while if it is more than 0.5, the Q value falls: these are thereforeundesirable. Furthermore, if z exceeds 0.4, the Q value drops severely;this is therefore undesirable.

Also, in the above compositional formula, if w and v are both zero, thepermittivity becomes low, and furthermore the temperature characteristicbecomes negative and the temperature characteristic cannot be controlledeven by addition of Eu, so it is desirable that w and v are not bothzero: at least either one of w or v should preferably have a positivevalue.

The properties of the dielectric ceramic composition of the presentinvention can be continuously varied between ∈=82.5 to 92.5, temperaturecharacteristic of frequency 10 to −20 ppm/° C. Excellent electricalproperties can thereby be conferred on resonance cavities of variousmaterials and sizes.

EXAMPLES Example 1

BaCO₃, Sm₂O₃, Nd₂O₃, Eu₂O₃, La₂O₃, Bi₂O₃, and TiO₂ powder of grain sizeof 1 μm or less, according to the compositional formulaBa_(6−3x)·{Sm_(1−y)·(Nd_(1−w−v)Eu_(w)Ln_(v))_(y−z)Bi_(z)}_(8+2x)·Ti₁₈O₅₄were blended and mixed with x=0.7, y=0.4, z=0.1, and v=(0.45, 0.4, 0.35,0.3, 0.25, 0), w=(0.05, 0.1, 0.15, 0.2, 0.25, 0.5) before molding underpressure of 1.5 T/cm² followed by sintering for three hours at 1370° C.in air and in a 100% O₂ atmosphere to manufacture dielectric ceramicswhich were used to produce 4.7 GHz band resonators whose properties areshown in Table 1.

Example 2

BaCO₃, Sm₂O₃, Nd₂O₃, Eu₂O₃, CeO₂, Bi₂O₃, and TiO₂ powder of grain sizeof 1 μm or less, according to the same compositional formula as inExample 1 were blended and mixed with x=0.7, y=0.4, z=0.1, and v=(0.45,0.4, 0.35, 0.3, 0), w=(0.05, 0.1, 0.15, 0.2, 0.5), before manufacturingdielectric ceramics under the same manufacturing conditions as inExample 1 which were used to produce 4.7 GHz band resonators whoseproperties are shown in Table 2.

Example 3

BaCO₃, Sm₂O₃, Nd₂O₃, Eu₂O₃, Pr₆O₁₁, Bi₂O₃, and TiO₂ powder of grain sizeof 1 μm or less, according to the same compositional formula as inExample 1 were blended and mixed with x=0.7, y=0.4, z=0.1, and v=(0.45,0.4, 0.35, 0.3, 0), w=(0.05, 0.1, 0.15,0.2, 0.5), before manufacturingdielectric ceramics under the same manufacturing conditions as inExample 1 which were used to produce 4.7 GHz band resonators whoseproperties are shown in Table 3.

Comparison

BaCO₃, Sm₂O₃, Nd₂O₃, Eu₂O₃, La₂O₃, Bi₂O₃, and TiO₂ powder of grain sizeof 1 μm or less, according to the compositional formulaBa_(6−3x)·{Sm_(1−y)·(Nd_(1−w−v)Eu_(w)Ln_(v))_(y−z)Bi_(z)}_(8+2x)·Ti₁₈O₅₄were blended and mixed with x=0.7, y=0.4, z=0.1, and v=0, w=0 beforemanufacturing dielectric ceramics under the same manufacturingconditions as in example which were used to produce resonators the sameas in the examples whose properties are shown in Table 1. Also, with theaforesaid compositional formula, dielectric ceramics of the compositionx=0.7, y=0.4, z=0, v=1, Ln=La were manufactured under the sameconditions as in the examples and their properties are shown in Table 1.

TABLE 1 v = 0.45 v = 0.4 v = 0.35 v = 0.3 v = 0.25 v = 0 w = 0.05 w =0.1 w = 0.15 w = 0.2 w = 0.25 w = 0.5 In air Qf (GHz) 7157 7175 71166935 6124 6003 ε 91.48 91.15 90.45 89.73 87.43 82.91 τf (ppm/° C.) 2.62−8.24 −5.38 −9.16 −12.36 −15.0 In Qf (GHz) 7181 7248 7155 6951 6238 6015100% O₂ ε 92.46 92.21 91.76 90.65 88.58 83.11 atmosphere τf (ppm/° C.)2.59 −3.22 −5.58 −9.00 −17.35 −19.9 w = 0 w = 0 v = 1 Composition v = 0Ln = La Comparison Qf (GHz) 6100 9000 ε 89.5 83 τf (ppm/° C.) −20 16

TABLE 2 v = 0.45 v = 0.4 v = 0.35 v = 0.3 v = 0 w = 0.05 w = 0.1 w =0.15 w = 0.2 w = 0.5 In air Qf (GHz) 7131 7118 7005 6510 6132 ε 91.0090.81 90.13 89.87 85.30 τf (ppm/° C.) 0.11 −6.21 −10.0 −14.2 −17.7 In Qf(GHz) 7136 7010 7018 6967 6389 100% O₂ ε 91.02 90.97 90.56 90.12 87.18atmosphere τf (ppm/° C.) 0.03 −8.35 −12.3 −14.8 −16.9

TABLE 3 v = 0.45 v = 0.4 v = 0.35 v = 0.3 v = 0 w = 0.05 w = 0.1 w =0.15 w = 0.2 w = 0.5 In air Qf (GHz) 7051 7003 6987 6513 6212 ε 90.3089.98 89.31 88.86 84.11 τf (ppm/° C.) −1.53 −7.18 −12.6 −14.3 −17.5 InQf (GHz) 7093 7096 7016 6888 6319 100% O₂ ε 90.88 90.54 90.02 89.5885.97 atmosphere τf (ppm/° C.) −2.30 −8.13 −12.9 −15.1 −18.24

INDUSTRIAL APPLICABILITY

In a BaO—TiO₂—Nd₂O₃—Sm₂O₃ based ceramics, by substituting some of theNd₂O₃ by Bi₂O₃ and furthermore by substituting some of the Nd₂O₃ byLn₂O₃ (where Ln=La, Ce, Pr), the properties ∈=88.5 to 92.5, Qf=6000 to7300 GHz, τf=3 to −10 ppm/° C. were obtained. Also, by substituting withEu₂O₃ instead of Ln₂O₃, a dielectric having the properties: ∈=85,Qf=6000 GHz, τf=−1.5 ppm/° C. can be obtained. Furthermore, by combiningthe aforementioned two effects, i.e. by substituting with Eu₂O₃ part ofthe substituted Ln₂O₃, improvement can be achieved to ∈=82.5 to 92.5,Qf=6000 to 7300 GHz, τf=10 to −20 ppm/° C.; in this way, excellentelectrical properties can be provided for resonance cavities made ofvarious materials and of large size.

What is claimed is:
 1. A microwave dielectric ceramic composition whosecompositional formula is represented by:Ba_(6−3x)·{Sm_(1−y)·(Nd_(1−w−v)Eu_(w)Ln_(v))_(y−z)Bi_(z)}_(8+2x)·Ti₁₈O₅₄(where Ln=La,Pr) where the values of x, y, z, w and v in thecompositional formula satisfy the following values: 0.5<x<0.8,0.3<y<0.5, 0<z<0.4, 0<w≦1,0<v≦1, y−z>0.